Malcolm Turnbull has said he will quit Australia's parliament on Friday following his ouster as prime minister by party rivals, local media report.
Mr Turnbull was replaced by Scott Morrison last week in a bid to end infighting that had crippled the centre-right government.
The ousted leader said Australians would be "appalled" by recent events.
His departure will trigger a by-election and place Mr Morrison's parliamentary majority at risk, according to a BBC report Tuesday.
In explaining his decision, Mr Turnbull again took a thinly veiled swipe at his predecessor, Tony Abbott - who had been accused of undermining the government.
"Former prime ministers are best out of parliament not in it, and I think recent events best underline the value of that observation," Mr Turnbull told party members on Monday, in a speech reported by multiple outlets.
Without Mr Turnbull, Mr Morrison will command 75 of a reduced 149 seats in the House of Representatives.
A by-election for Mr Turnbull's seat will most likely take place in October, Australian media reported.
If the government loses the seat, Mr Morrison will be forced to rely on independents to pass legislation in a 150-member parliament. The Labor opposition currently has 69 seats.
The seat, Wentworth, has been held by the conservative Liberal Party since World War II. However, some say victory for the government is not guaranteed.
In a further twist, Mr Abbott's sister, Christine Forster, is reported to be considered running for the seat - but must first be selected by the Liberal Party.
The next general election is due to be held by May, with opinion polls currently giving Labor the lead.
